People performing tasks in an environment where a medium to high level of ambient noise can be encountered are required to have some form of hearing protection. Normally, a circum-aural or in-the-ear hearing protection device is employed.
When using a hearing protection device, situational awareness is reduced. Situational awareness can be restored by adding a “talk-through” function to the hearing protection device. The talk-through function allows the user of the hearing protection device to hear sounds external to the device, without having to remove the device. The typical method of adding the talk-through function is to add a microphone that samples the ambient environment. The signal from the microphone is passed to a talk-through circuit, which passes an electrical signal to a speaker and thus onto the user's hearing.
Any device that uses one or more microphones to sample the ambient environment is susceptible to noise being introduced into the microphone(s) as a result of wind. Wind acts upon a microphone in a similar way as sound pressure waves and is therefore hard to distinguish from sounds. Numerous technical and white papers detail how wind affects microphones. Particular examples are convention papers 5718, 6624, 6635 and 6879 published by Audio Engineering Society.
The greater the wind speed the greater the amount of wind noise induced into a microphone, until the wind speed reaches a level where sounds picked up by the microphone are distorted beyond recognition. The greater the speed of the wind the wider the frequency band of wind noise induced into a microphone.
Wind, by its nature, exists in a non-predictable chaotic state and can induce noise in a microphone across a broad spectrum of audio frequencies. When wind encounters obstacles, turbulence is introduced into the wind flow. The turbulence can act in a similar manner to sound and can therefore be interpreted by a device using a microphone as sound. Turbulence exacerbates the problem of wind noise.
For the purposes of simplifying the explanation of turbulence (in the context of wind hitting a person's head), an example situation is considered in which wind is blowing directly into the face of the person, which wind is homogenous and turbulence free prior to encountering the person.
With reference to FIGS. 1a, 1b and 1c, a partial horizontal cross section of the person's head (with no hearing protection device present) is used as a basis for the explanation. This is not to be viewed as an accurate representation of the person's head, it is used to illustrate principles only. The cheek (101), tragus (102), ear canal (103), ear drum (104), concha (105), the rear face of the concha (106) and the helix (107) are used as reference points.
As shown in FIG. 1a, when wind hits the cheek (101), (or similar part of the head), turbulence (202) is created within the wind. The turbulence (202) created has a length that can causes a microphone to interpret it as a low frequency audio sound.
As shown in FIGS. 1b, when wind hits the helix (107), turbulence (302) is created within the wind, which turbulence can be interpreted by a microphone as a medium frequency audio sound.
Finally, as shown in FIG. 1c, when wind hits the tragus (102), turbulence (402) is created within the wind, which turbulence can be interpreted by a microphone as a high frequency audio sound.
Research carried out by the National Acoustics Laboratory of Australia determined the wind turbulence around the ear for different wind directions and the resultant frequencies induced into a microphone. In accordance with the research, all of the turbulences within the wind created by a head, including those example turbulences in FIGS. 1a, 1b and 1c, which are shown for the purposes of explanation only, are eventually damped to zero, but the turbulences cover sufficient distance to affect any microphone near the ear.
The reduction of wind noise in microphones is a primary goal of all devices where wind can be encountered, however, to date, no suitable solution has been provided for reducing wind noise to an acceptably low level when one or more microphones are provided in an earpiece, which may be used for an in-the-ear hearing protection device or otherwise.
A prior art earpiece provided with a microphone for picking up ambient sounds is known from US 2010/0166204. Whilst this document purports to position a microphone pick-up opening so that it is not affected by wind noise, the arrangement is not effective in reducing wind noise since the microphone pick-up opening is provided on an outer face of the earpiece such that the microphone directly samples the ambient environment outside the concha.